Sierra Nevada Aquatic Research Laboratory

26 Jun, 06 AM - 21 Jul, 10 AM

Purpose of research project: The moraines in the Deer Lake Drainage occur at an anomalous altitude above Tioga age moraines (assumed to be Pleistocene glacial maximum) and below the late Holocene Little Ice Age advance around 1000 ybp. Their presence suggests a glacial advance occurring sometime in the late Pleistocene (Younger Dryas), a time considered a global cooling event evidence of which has not been found in the Sierra Nevada. Since mountain glaciers provide a sensitive indicator of climate change, particularly the balance of winter storm frequency in the Sierra, this glacial record could provide insight to the Sierra?s relationship with global conditions. Deer Lakes close proximity to Mammoth Pass provides them unique sensitivity to Pacific climate conditions due to its ability to channel storms. The intent of this study is to reconstruct the paleoclimate history of the Deer Lakes moraines through a combination of lake core analysis, mapping, and geomorphic analysis. Project Description: Understanding changes in modern climate in the Sierra Nevada is necessary for predicting possible future changes caused by global warming trends. A better understanding of the dynamics of the global climate system can be achieved through the study of the paleoclimate record in the Sierra Nevada in conjunction with the North Atlantic record contained in ice cores. Understanding those changes and relationships can lead to predictions and preparations for possible future climate change. With likely future warming in the next century, will precipitation and water supply to the Sierra Nevada, Owens Valley and dependent Los Angeles metro region likely increase or decrease? These climate records provide a means of testing predictive climate models. The Sierra Nevada contains a record of climate change evident in the form of moraines and lake sediments recording ice advance and retreat going back 2.7 mya (Gillespie and Zehfus, 2004). Currently the last Pleistocene advance found in the Sierra dates to 14 ka leaving the global cooling event, the younger Dryas, evident elsewhere in the northwest and in Greenland ice cores (Benson et al., 1997), but absent in the Sierra Nevada (Gillespie and Zehfuss, 2004). Greenland Ice Core Project 2 (GISP2) uses climate proxy data (oxygen isotopes) to infer paleoclimatic conditions in the north Atlantic and has shown evidence of a cooling event during the Younger Dryas period 11 ? 10 ka (Bjorck, et al., 1998). This event coincides with terrestrial records found in Europe and the northwest United States. The interaction of climate is spatially complex, therefore in some instances a large scale climate shift on short time scales, such as the Younger Dryas event, may not be seen in some regional proxy data or show a time lag making the response diachronous (Bjorck, et al., 1998). Mammoth Pass is a unique location in the Sierra Nevada range in that it lies in a maritime mountain climate zone, and is at relatively low elevation point (2900-3363 m) in the mountain chain (Burak and Davis, 2001). This low elevation allows winter Pacific storms that have produced snowfall amounts exceeding a meter in a 24 hour period (Burak and Davis, 2001). The glacial moraines of Deer Lakes have not been studied, and may provide evidence of a glacial advance of the Younger Dryas global climate event that has previously not been observed in the Sierra Nevada. This is suggested by their anomalous equilibrium line altitude above Tioga age ELA (700 m below modern ELA) and below the Matthes ELA (60 m below modern ELA) (Clark and Gillespie, 1997). Deer Lakes? close proximity to (approx. 5 mi south) Mammoth Pass would provide it with greater sensitivity to a global climate shift than other drainages in the Sierra Nevada chain. I hypothesize that these moraines are a record of a Younger Dryas advance due to its unique location showing synchronicity with the global trend of 11 ka. The moraine sequence at Deer lakes provides a unique opportunity to correlate the terrestrial climate record (moraines) with a lacustrine record in three post-glacial lakes dammed by terminal moraines within the same isolated drainage. The intent of this study is to accurately date and compile a comprehensive sequence of events for this ice advance obtained and analyzed through carbon dating organic sediments, clast type and size analysis, loss on ignition, and magnetic susceptibility analysis on lake cores in conjunction with a geomorphic analysis and mapping of the moraine sequence. Similar studies by Dahl et al. (2003) have been used to monitor the advance of a modern glacier using lake cores near the Hardangerjokulen glacier in Norway (Dahl et al., 2003). Those techniques used that will be applied to this project are described herein. Magnetic susceptibility in conjunction with clast size and type, along with, loss on ignition for carbon content, provide a potential record of ice advance. Glacial movement is evidenced by the presence of course grained sediment containing magnetically susceptible clasts derived from glacial scouring of bedrock. Retreat of the glacier is shown through an increase in organics and finer grain deposition and a decrease in magnetic susceptibility (Dahl et al., 2003). If the oldest layers in the lake can be constrained by carbon dating of organics present in the sediment, then the timing of the ice withdrawal allowing that lake to form is possible. Mapping and grouping of moraines will be done using the same criteria and technique as Berry (1992) (with the exception of satellite imagery used in this study) through geomorphic analysis, soil development, vegetation, boulder counts (size and number), moraine source rock identification, and description of surface clast weathering and relief. This process will provide a general understanding of exposure relative to other moraines in the vicinity. Also, stratigraphic relationships with other advances will be analyzed if appropriate and compared to more extensively developed moraine systems at lower altitudes in the same watershed, assumed to be Tioga in age. Mapping will require about a month?s time at the Deer Lakes field area in order to accurately compile the necessary data. To do this I will stay at a research station near the field location and camp on days when weather permits. A 40 minute drive and a 6.5 hour hike to and from the field area every other day will be required.

Visit #20861 @Sierra Nevada Aquatic Research Laboratory

Approved

Under Project # 21398 | Research

Paleoclimate history of the Deer Lakes moraine series, Sierra Nevada, California

graduate_student - University of California, Riverside

Reservation Members(s)

Daryl Kohut Jun 26 - Jul 21, 2010 (26 days)
Daryl Kohut Jun 26 - Jul 21, 2010 (26 days)

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Dorm 2 Jun 26 - Jul 21, 2010